Report: Ancient mass extinction happened suddenly

An asteroid collision is one of the suspected causes of the mass extinction

By Richard StengerCNN

(CNN) -- A cataclysmic event quickly killed off most of the species on Earth about 200 million years ago, after which dinosaurs began their long reign on the planet, according to a report to be published in Friday's edition of the journal Science.

"This mass extinction has been known for a long time, but this is the first study to show that it happened suddenly," said paleontologist Peter Ward, lead author of the report.

"This is the first time that we can see how sudden the event was. It was very quick. Not a long, protracted episode."

Researchers found evidence of the rampant die-off, which took place on the boundary of the Triassic and Jurassic periods, by studying the fossil record of common marine plankton from the era.

Between 50 and 80 percent of life on the planet didn't survive the catastrophic period, which lasted less than 10,000 years -- the blink of an eye in geological terms.

Various causes suspected; dinos spared

An asteroid collision, like those thought to have sparked other large-scale extinctions over the ages, is among the suspected causes of the episode. One such event 65 million years ago ended the age of dinosaurs.

A sudden change in climate induced by a burst of volcanic activity may also have triggered the event. Ward and his colleagues noted that the die-off took place just before the breakup of Pangea, a supercontinent that included all the landmasses on Earth.

Curiously, the extinction killed off mammal-like reptiles that once roamed the Earth, but spared the dinosaurs, according to the report. "Perhaps creatures reproducing with buried eggs survived and large animals with live births did not," Ward speculated.

The researchers from the United States and Canada trudged through thick forests on remote islands off British Columbia to gather fossil evidence showing sharp, correlating collapses in organic carbon -- a marker of plant life productivity -- and radiolarians, single-cell organisms that served as a food source for many marine species.

"These provide the best report of how nasty the extinction was at this boundary," Ward said.